A COM port redirector (tty port redirector under Unix/Linux) is specialized software (often including device driver and user application) that includes the underlying network software necessary to access networked device servers that provide remote serial devices or modems.
Overview[edit]
The purpose of the redirector is to make the virtual COM port exhibit behavior that closely resembles that of a 'real' COM port, i.e., a COM port driver for local serial port hardware. A virtual COM port itself is a relatively simple software mechanism that can be implemented by driver software similar to that of a conventional COM port driver. The main challenges arise in two other areas: the network connection to the device server and the behavior of the device server. These issues are described in the Technology section below.
Vspe Virtual Serial Port Emulator
Applications use a COM port redirector through one or more virtual COM ports that the redirector creates, as configured by the user. When the application opens the virtual COM port, the redirector makes an IP network connection to the device server at the specified IP address and TCP/UDP port number that corresponds to the remote device on the server. The COM port redirector then begins relaying the application data stream between the virtual COM port and the device server.
A redirector will typically permit creation of many (at least 256) virtual COM ports, but simultaneous use of hundreds of ports is often practically limited by a number of factors, including the memory and processor requirements of the redirector, limits on operating system resources, and the performance of the network stack.
A redirector for the Windows operating system is typically configured using a control-panel style graphical user interface for creating virtual COM ports, configuring settings for individual COM ports, and configuring global settings affecting all COM ports. The redirector GUI typically also includes displays of virtual COM port activity and various diagnostic aids.
The performance of a COM port redirector is determined by both its implementation and the network it uses to reach device servers. The performance drawbacks of simple redirector implementations can be largely addressed by kernel-level drivers that avoid context switches. Network packet loss or excessive packet times have dramatic effects on redirector operation and must be avoided.
COM port redirector software products have been offered by at least 30 vendors dating back to the early 1990s. Compatible networked device servers are currently available from a large number of manufacturers, with a heavy concentration of revenue in the top players, who are based in the North America and Asia/Pacific regions.
The equivalent software for a Unix/Linux operating system is commonly called a tty port redirector and most of the information on this page also applies to it.
Redirectors address a number of issues related to the network connection, including:
Redirectors must also deal with the feature differences of networked device servers related to:
Because COM port redirectors emulate COM ports on the operating system abstraction level, rather than hardware serial ports, old software which is not written to utilize the operating system, but instead interface directly with a serial microcontroller (hardware ports 0x3F8 to 0x3FF for COM1, for example) will not function with COM port redirectors.
Variants[edit]
Specialized types of redirectors have been offered to meet the needs of certain applications.
A redirector may support back-to-back operation, in which two computers run copies of the redirector and an outbound connection from one results in an inbound connection to the other. In effect, this technique creates a serial communications tunnel through a network connection. In practice, this configuration works only for certain applications but offers potentially lower costs and higher performance using the Internet to carry serial communications instead of modems between two computers.[citation needed]
A redirector may include a modem emulator that allows the application to use 'AT' modem commands even though no physical modem is present. The 'number' dialed is an IP address, and the connection is a TCP network connection instead of a modem telephone call. This type of redirector is generally used by applications in originating client software needs to use a modem but the destination for the connection is a network endpoint. Back-to-back operation of this type of redirector can, in some cases, function as a replacement for modems on two computers for some applications. Network effects on timing of the data stream generally preclude the use of this method for transmitting faxes. Additionally, this method is also not reliable if used for PPP connections (such as dial-up networking) due to architectural limitations of TCP, a topic discussed in technical literature related to TCP-over-TCP.
Virtual serial port[edit]
One variant of a COM port redirector is a virtual serial port. A virtual serial port is a redirector without network software support which is usually used to create a pair of back-to-back virtual COM ports on the same computer. Two legacy applications can then communicate using virtual serial ports instead of conventional inter-process communication mechanisms such as named pipes.
This type of software is capable of emulating all serial port functionality, including Baud rate, data bits, parity bits, stop bits, etc. Additionally, it allows the data flow to be controlled, emulating all signal lines (DTR / DSR / CTS / RTS / DCD / RI) and customizing pinout.
Serial port emulation[edit]
Specification[edit]
See also[edit]References[edit]
SerialToIP - open source Terminal Server software
Further reading[edit]
Retrieved from 'https://en.wikipedia.org/w/index.php?title=COM_port_redirector&oldid=859694748'
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Virtual COM Port Driver emulates virtual serial ports and connects them in pairs via virtual null modem cable. Applications on both ends of the pair will be able to exchange data in such a way, that everything written to the first port will appear in the second one and backwards.
All virtual COM ports work and behave exactly like real ones, emulating all their settings. You can create as many virtual port pairs as you want, so there will be no serial ports shortage and no additional hardware crowding your desk. Moreover, Eltima virtual serial port technology can be fully integrated into your own software (DLL, ActiveX or Core level usage).
Built on Virtual COM Port Driver functionality, Virtual COM Port Driver PRO is an efficient, powerful software application. It assists in creating bundles of virtual serial ports and allows the user to customize port parameters, making it an ideal solution for many different uses. Virtual Serial Port Driver PRO offers a user-friendly way to manage both real and virtual COM ports.
Virtual COM port software is a perfect solution to create an unlimited number of virtual COM ports, which completely emulate real serial port parameters and behavior.
Create any number of virtual COM ports
Virtual COM Port Emulator provides you with the ability to emulate an unlimited number of virtual COM ports. Created RS232 virtual ports are located in 'ports' group in Device Manager, which means that they will be visible and easily recognized by all software and hardware you install. No real hardware serial ports are occupied.
Complete real ports settings emulation
Virtual RS232 ports, created by Serial Port Emulator utility, work exactly like real ones. They emulate all real serial ports settings and provide strict baudrate emulation and full HandFlow control support. Additionally, you can easily emulate a serial line break (only for Standard License). Moreover, VSPD uses advanced Windows kernel driver technology, which ensures WDM, WMI, Power Management, PnP, etc. support. Virtual COM Port Driver is fully compatible with API COM and supports all Windows messages.
Manage all signal lines
Virtual serial ports created with Virtual COM Port Driver emulate and support all standard hardware signal lines (DTR/DSR, RTS/CTS, RING, ERROR, DCD, etc.). As in real null modem connection, DTR of the local port is connected to DSR and DCD of the remote port, and RTS of the local port is connected to CTS of the remote port. Moreover, you can choose loopback pinout or create custom one depending on your hardware configuration (only for Standard License).
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Throughout its long history, our software has helped a lot of people to solve a variety of tasks and problems of absolutely different kinds. And here are some of them:
Now it is especially hard to develop an application which works with a serial device, considering that not every modern PC has a serial port to connect that hardware. The least convoluted way is to create a virtual serial connection, and Virtual Serial Port Driver does exactly that.
Kenneth Floyd, Embedded Systems Software DeveloperLucy Williams, Application Integration EngineerPatrick Reynolds, Computer Laboratory Technician
Virtual Serial Port Driver
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COM ports have been introduced a long time ago and have been an integral part of computers. These days however they become almost obsolete as more and more machines use USB ports or no ports at all. This doesn't eliminate the need for serial connections though, especially if we are talking about industrial equipment, lab devices, etc. Developers creating software to work with industrial devices need to test and debug applications before releasing them. That's where virtual serial port emulation comes into spotlight. If you are looking for a software to create a virtual COM port on Windows 10 or a virtual COM port on Windows 7 read about the virtual serial port emulator software that we consider to be the top solutions currently offered:
Contents
1. Virtual Serial Port Driver developed by Eltima Software allows users to create virtual serial ports that can be connected in pairs via virtual null modem (com0com) cable. Applications communicating with created virtual ports treat those ports the same way they would communicate with real ports. This software solution works on 32- and 64-bit Windows OS and supports operating systems up to the latest Windows 10. Virtual Serial Port Driver is officially signed by Microsoft.
Virtual Serial Port Emulator Software
The advantages of Virtual Serial Port by Eltima:
In case you are willing to split a real or virtual COM port data between several applications, check out our tutorial about serial port sharing with VSPD PRO version.
2. Null-modem emulator (com0com) is an open source kernel-mode virtual serial port emulator for Windows, distributed under GPL license. One can create an unlimited number of virtual serial port pairs and connect one serial application to another with any created pair. This app can provide serial interface for device emulators and serial port redirectors.
See comparison chart of Virtual Serial Port Driver and Null-Modem Emulator
3. Free Virtual Serial Ports by HDD Software is a Windows user-mode software that offers creation of virtual COM ports and emulation of physical serial ports. This app operates in user-mode exclusively and acts as a hardware COM port with full functionality, baud-rate emulation, configuration of data bits, parity, stop bits, XON/XOFF flow control, etc.
This serial port emulation software works on Windows desktop and server versions up to Windows 8/8.1 32- and 64-bit.
4. Virtual Serial Ports Emulator developed by Eterlogic is the next VSPE solution on our list. It is developed for software developers to create/debug/test applications that use serial ports. Virtualization of ports offers great possibilities: same device can be opened by different apps, physical serial port data can be shared among several applications, a serial port can be shared to local network (via TCP), one can create virtual serial port pairs, etc. This program supports Windows 2000, XP, Vista (32/64), Windows 7. Licenses for 32-bit platforms are offered for free, while 64-bit solution is paid.
5. Virtual Serial Port Kit is developed by FabulaTech and offers virtual serial ports creation with the possibility to connect them via virtual null-modem cables. All information written to one virtual port is immediately available on the other one of the pair. Virtual serial ports function the exact same way as hardware serial ports. This app also runs as system service meaning all virtual ports are available prior to user logon.
Prices and more details are available on developers' websites. Some solutions are free, but will require you to expose your source code when developing an app with them, also not offering support for the latest Windows OS. Some solutions require a payment but in return you receive an up-to-date software with regular updates and dedicated support service. Hopefully this brief overview will help you get the best virtual COM port solution for your project.
COM Port Data Emulator
This software tool allows the user to emulate the data stream generated by a serial interface or device. You can use the application to create data packets and send them to network-connected serial ports. The data packets can be randomly generated or read from a file to enable complete control of their contents.
The program offers flexible configuration options and can serve as a server or client on a TCP/IP network. Full duplex mode and flow control are supported on COM and RS232 ports. Log files of sent data can be saved for future analysis and data is visually displayed as it is sent and received. Developers and network professionals can benefit from the features of this serial communication application.
Virtual Serial Port DriverVirtual Serial Port Emulator 64-bit
Requires: Available on Windows , 5.5MB size
Version 9.0.575 (23rd May, 2019) Release notes Category: CommunicationApplication
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